Handling double submit at server side, displays balnk page.

[Waez Ali]

Hi,

My aim is to display expected page to user and process his request only once despite double submits.

I am able to detect double submit using Token Synchronization and now my porblem is to handle the duplicat requests after I detect them. Please see the code below.

I tried saving the ServletResponse in session and locking it, when done with the first request other waiting threads would pick up the saved response object and will try to write its content through the response object of last submitted request.

But the successful If condition doesn't work as I thought of working...instead it displays blank page.

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {					
		HttpSession session = ((HttpServletRequest)request).getSession();
		if(DoubleSubmitUtils.checkDoubleSubmit((HttpServletRequest)request,(HttpServletResponse)response)){			
			System.out.println("Is Duplicate Request ");
			// When first request is done pick up the saved object and write it back to browser
			synchronized(session){											 
				HttpServletResponse first_response =(HttpServletResponse)session.getAttribute("FIRST_REQUEST");				
				 if(first_response != null){
				 	ByteArrayOutputStream bos = new ByteArrayOutputStream(); 
					try {
						bos.writeTo(first_response.getOutputStream());						
					} catch (IOException e) {		
						e.printStackTrace();
					}				 		 	 
				 	((HttpServletResponse)response).getOutputStream().write(bos.toByteArray());				 					 	
				 }
			}										
		}else{
			//Not a duplicate request so process further 
			synchronized(session){					
				//Release object from session
				if( null != session.getAttribute("FIRST_REQUEST") ){				
					session.removeAttribute("FIRST_REQUEST");
				}
				session.setAttribute("FIRST_REQUEST", ((HttpServletResponse)response));
				chain.doFilter(request, response);
				System.out.println("DONE WITH THE CURRENT REQUEST");
				session.notifyAll();
			}			
		}		 
	}    

Please suggest.

Thanks.

[Waez Ali]

Any input on this one please !! Would be much appriciated.


Regards,
Waez.

[Ananth Chellathurai]

I would restrict double submit in the client side rather at the server side. http://www.willmaster.com/library/demo/singleclick.php could help you to do that.

Regards
Ananth Chellathurai